java - Output breaks as input parameter increase in size -

i writing basic program takes parameter , calculates product of odd numbers based on parameter.

it works if pass 1 19 @ 20 output negative number , @ 35 0??

i'm sure there wrong in algorithm?

suggestions:

import java.util.arraylist; import java.util.list;   public class productofintegers {  public static void productofoddintegers(int i){     int[] numbers = new int[i];     for(int j = 0; j < numbers.length; j++){         numbers[j] = j + 1;     }     list<integer> oddnumbers = new arraylist<integer>();     for(int j = 0; j < numbers.length; j++){          if(numbers[j] % 2 != 0){             oddnumbers.add(numbers[j]);         }     }            int product = 1;     for(int n: oddnumbers)         product*=n;     system.out.println(oddnumbers);      system.out.println(product);  }  public static void main(string [] args){     productofoddintegers(15); } 

}

calculates product of odd numbers based on parameter.

no program calculates product of numbers.

this being said, algorithm rather inefficient: instead of first generating array of integers, filtering , calculating product, can use single for loop:

public static long productofoddintegers(int n){     long prod = 1;     for(int = 3; <= n; += 2) {         prod *= i;     }     return prod; } 

you better use long since such products can rather huge. scales root of factorial after all.

you can use biginteger approach can use arbitrary n:

public static biginteger productofoddintegers(int n){     biginteger prod = biginteger.one;     biginteger bin = new biginteger(""+n);     biginteger 2 = biginteger.one.add(biginteger.one);     for(biginteger = two.add(biginteger.one); i.compareto(bin) <= 0; = i.add(two)) {         prod = prod.multiply(i);     }     return prod; } 

jdoodle demo

it furthermore bad design println commands in methods. should make separation between calculating , printing.